I use a work PC, my HP, and a laptop. Xmarks has been good at keeping my bookmarks and passwords secure and supports a revision history of your changes. Somehow I messed up my bookmarks and this got moved to the Xmarks server. Not a problem, I just rolled back to an earlier revision and got all of my bookmarks back.
It’s like applying SVN onto my browser. Mozilla Weave is not quite like that. It does do bookmark and password synchronization but it doesn’t provide a means to rollback to an earlier version of your bookmarks (or maybe I just couldn’t find it). What appeals to me is that it also syncs up your browsing history. I have often been at work trying to remember a web site I had seen the night before at home. I’m hoping that this will sync my browsing history.
Xmarks has been very responsive to their users so I expect this feature to make it into their extension soon.